For many plant species there are well known protocols for the regeneration of whole plants from the aseptic culturing of an originally undifferentiated tissue such as protoplast, callus, or meristimatic tissue. Often, the protoplast, callus or meristimatic tissue have been genetically transformed or the meristimatic tissue is selected from a desired patented stock. The resulting protoplast, calli or tissue can then be regenerated into whole plants, including whole fertile plants that can grow in soil.
Existing methods of aseptic plant culturing involved starting with a callus or other stock material which is subcultured on a periodic basis onto a suitable fresh medium so as to induce embryo formation. As embryos are formed, they are removed and plated onto a second medium containing suitable plant growth regulators designed to bring about embryo maturation. Through periodic transfers onto fresh mediums, embryos can be differentiated into plantlets which are then transferred to another solid growth medium where root systems can be grown.
Alternative methods of plant regeneration or micropropagation involve the use of liquid cultures which immerse the various stages of the regenerating plant. While liquid culturing may be used to bring about mature viable plants, the process is expensive, prone to contamination, and requires that special steps be undertaken to successfully transfer the plants from a liquid culture environment to a condition where the plants are viable in a freestanding soil environment. In particular, the use of liquid cultures on rotary shakers results in a high shear force in the culture media. As vessel size increases, the high shear force involved in aeration creates an environment unsuitable for the growth and development of embryos and delicate organs such as leaves and shoots.
In particular, the collection and transfer of propagated embryos continues to be a labor intensive, manual process in which individual embryos are manipulated using forceps. While more mechanized solutions have been proposed, none have met with commercial success given in part the expense and complexity of the handling equipment.
It is also known in the art to propagate plant tissue into small plantlets as is taught in U.S. Pat. No. 5,597,731, incorporated herein by reference. The above patent discloses a plant propagation system in which sealed membrane vessels are used as a container for a plant material therein. The translucent vessels are permeable to gas and liquids. They are suitable for cultivating plant tissue obtained from a parent plant and which is subsequently grown heterotrophically. Once the plant material has developed the capability to photosynthesize, the sealed vessels are transferred to a greenhouse environment for photoautotrophic growth. An appropriate amount of needed gases, water, and liquid nutrient solution can be supplied in a controlled manner to the vessel trays.
Other plant propagation systems are known which use a liquid nutrient solution as set forth in U.S. Pat. No. 5,558,984, incorporated herein by reference. While a liquid nutrient solution for propagation of plant tissue offers numerous advantages in the large scale and economical propagation of plants, there remains room for improvement and variation within the art.